Proteins with covalently bound heme or linear tetrapyrrole (bile pigment) prosthetic groups are present universally in having organisms. These proteins function in electron transport, photochemistry, and many other roles. This research is directed at the determination of the structure, stereochemistry, and biosynthesis of protein-bound tetrapyrroles with specific focus on biliverdin-derived bilin prosthetic groups of the phycobiliproteins. Small peptides bearing tetrapyrrole prosthetic groups will be isolated in pure form and their structure and stereochemistry determined by a combination of techniques, including 1H NMR, fast atom bombardment mass spectrometry, circular dichroism, and, where possible, by comparison with reference compounds, either derived by degradation of tetrapyrrole-bearing proteins with known crystal structures, or by synthesis. A sensitive in vitro fluorescence assay has been developed for the measurement of the addition of linear tetrapyrroles to apophycobiliproteins and will be utilized for the detection of precursor compounds and enzymes involved in their synthesis and attachment to the polypeptides. Molecular genetic approaches to the identification of such enzymes have also been devised.